PROJECT SUMMARY: Circadian clocks are important regulators of cellular functions and homeostasis. Age- related alterations in the human circadian system are implicated in neuronal pathologies. Recent evidence in fruit flies and mice suggests correlation between disrupted rhythms and neurodegeneration; however, very little is known about mechanisms involved. To address these mechanisms, we compared circadian transcriptome in heads of young and old Drosophila using RNA-seq. We found that several genes that were expressed in young flies in a rhythmic fashion lose cycling pattern to become constitutively low or high in old flies. We uncovered a group of genes, which were low and arrhythmic in heads of young flies but became strongly rhythmic in heads of old flies. This group contains known stress-responsive genes that are induced in young flies in response to oxidative stress or hypoxia. Based on our preliminary data, we hypothesize that clock orchestrates rhythmic expression of neuroprotective genes, which we termed late life cyclers (LLCs), in response to intrinsic stress and damage in the aging nervous system. In Aim 1, we will measure genome-wide binding of the core circadian transcription factors CLK and CYC through ChIP-Seq and identify age-specific binding events that could be responsible for these regulatory changes. In Aim 2, we will measure chromatin modifications H3K4me3 and H3K27me3 as well as RNA Polymerase II binding using ChIP-Seq around the clock in young and old fly heads to characterize the effect of age-altered chromatin state and transcriptional changes associated with aging. In Aim 3, we will measure microRNA expression around the clock in young and old flies, to identify age-altered microRNA regulatory events that could result in post-transcriptional changes in rhythmic gene expression. The proposed work should reveal clock-controlled pathways that protect brain from age-related damage. Given the conserved molecular basis of circadian clock and aging biology, we expect these pathways will also function in humans. !